Data can evolve over time. In many applications there is a need to retrieve a previous data version. One of these applications is the continuous data protection (CDP) application. U.S. patent application publication serial number 2005/0066118 of Perry et al., and U.S. patent application publication serial number 2005/0193272, all being incorporated herein by reference, describe prior art devices and method for continuous data protection.
Various data structures were suggested for tracking the evolution of data over time. The following articles, both being incorporated herein by reference, illustrates two data structures known as the B-tree and the BTR-Tree: “The BT-Tree: A Branched and Temporal Access Method”, Jiang, Salzberg, Lomet, Barrena, Proceedings of the 26th VLDB Conference, 2000; “The BTR-Tree: Path-Defined Version-Range Splitting in a Branched and Temporal Structure”, Jiang, Salzberg, Lomet, Barrena, Symposium for Advances in Spatial and Temporal Databases, 2003.
These branch temporal indexes can be maintained if certain assumptions are fulfilled. According to a first assumption entries of the branch temporal indexes are inserted in order of increasing timestamp.
In addition, the update of these structures can be relatively complex and involve duplicating data and even metadata. In addition the maintenance of these data structures may require reference counters.
The following U.S. patent applications and U.S. patents, all being incorporated herein by reference, also describe various methods for managing data: U.S. patent application publication serial number 2005/0066222 of Rowan et al., U.S. patent application publication serial number 2005/0076262 of Rowan et al., U.S. patent application publication serial number 2005/0065962 of Rowan et al.; U.S. patent application publication serial number 2005/0063374 of Rowan et al.; U.S. patent application publication serial number 2005/0076264 of Rowan et al.; U.S. patent application publication serial number 2005/0066225 of Rowan et al.; U.S. patent application publication serial number 2005/0076261 of Rowan et al.; U.S. patent application publication serial number 2005/0066118 of Perry et al., and U.S. patent application publication serial number 2005/0071379 of Kekre et al., and US Patent Application publication serial number 2004/0117572 titled “Persistent Snapshot Methods”.
There is a growing need to provide devices, computer program products and methods that will enable to manage data, especially using write-back cache units.